The monitoring and maintenance of a physiologically suitable body climate and here especially of the status of the body fluids is very important for well-being especially in persons who are subject to physical stress such as, for example, firefighters. During missions, such persons wear protective clothing or clothing parts that offer protection against the environment and may be fire-resistant.
Such special clothing has, for example, according to DE 195 47 795 C2 (corresponding to U.S. Pat. No. 5,774,902), an outer protective layer, which offers protection against undesired effects from the outside, an inner layer permeable to moisture and/or vapor and a distance-maintaining spacer layer, which is permeable to fluids, is arranged between the outer protective layer and the inner layer and can be climatized by introducing a fluid.
DE 10 2004 011139 A1 (corresponding to U.S. application Ser. No. 10/979,713) discloses a device for body climate control with:    a piece of clothing with ventilating ducts, which are connected at their inlet and outlet to the environment, with at least one temperature sensor, which detects the body temperature of the wearer of the piece of clothing, with a fan, which admits ambient air into the ventilating ducts, and with a measuring and analyzing unit, which is connected to the at least one temperature sensor and the fan.
Besides the risk of thermal and physical overload, members of mission crews performing hard physical work, especially firefighters, run the risk of dehydration. An aggravating circumstance is that the loss of water is manifested in a drop in performance capacity and increase in the body core temperature. A fatal circulatory collapse may develop due to these causes, especially in case of long mission times.
Attempts at describing the actual moisture balance under mission conditions by means of physiological models have not been successful and are not suitable for the conditions of practical use.